"We will not fail in our fight against this disease through lack of resources," he said, after the Government brought in immediate restrictions on the movement of ash trees.

He spoke to MPs after Owen Paterson, the Environment Secretary, imposed an immediate ban on imports to halt the spread of the disease, which has killed 90 per cent of ash trees in Denmark.

Mr Paterson, who took on the job last month, promised the Government's swift action will "protect our native trees" from the fungus.

Labour has accused the Coalition of being "asleep on the job" since the disease was first discovered in nurseries earlier this year and in the wild in June.

Mary Creagh, Labour's shadow environment secretary, said: "The question on everyone's lips is why did it take so long? Why did ministers sit back and cross their fingers and wait until it was found in the wild in June?"

She accused the Goverment of threatening Britain's forests by cutting the budget of authorities that look after tree health.

Mr Heath said: "There has been no reduction in the resources applied to plant health and tree health in this country."

He said ministers are taking "all necessary precautions" and criticised Labour for looking for someone to blame.

About 100,000 trees have already been burned to stop the spread of the fungus, amid fears it could cause as much damage as Dutch elm disease in the 1970s.

Speaking at Cannock Chase, in Staffordshire, Mr Paterson assured people he is taking the problem very seriously.

“This is a very serious disease that demands action to stop its spread. I have ordered both an import ban and movement restrictions on trees from infected areas. This comes into force immediately.

“Work is already underway to tackle the disease. Plant health authorities have been monitoring trees in infected areas to ensure early detection and trade bodies have been encouraging their members to impose voluntary import bans. By working together we can protect our native trees from this devastating disease.”

The disease leads to leaf loss and has already affected trees in England and Scotland. The ban is being put in place before the main planting season gets underway in late November.

Movement restrictions will also be imposed, so that trees from infected areas will not be able to be moved to other locations within the UK.

Officials urged people to report suspected cases of ash dieback to the Forestry Commission.

The scientist in charge of tackling the fungus said last night it could "change the countryside significantly".

Professor Ian Boyd, chief scientific adviser at the Department for Environment, Food and Rural Affairs, said: "In general we have to accept that this is a bit of a disaster for our ash trees.

He told the BBC: "Ecologically it is going to change the countryside very significantly. Parallels have been made with Dutch elm disease of the 1970s."